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Chapter 16

Chapter 16 - Evolution and Human Behaviour.docx

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McMaster University
Jon Stone

1Chapter 16 Evolution and Human BehaviourWhy Evolution Is Relevant to Human BehaviourThe application of evolutionary principles to understanding human behaviour is controversialAll phenotypic traits including behavioural traits reflect the interactions between genes and the environmentoThe naturenurture debate is based on a false dichotomyoIt assumes that there is a clear distinction between the effects of genes and the effects of the environmentoHowever gene are not like blueprints that specify phenotypeoEvery trait results from the interaction of a genetic program with the environmentoThe expression of any genotype always depends on the environmentoThe expression of behavioural traits is usually more sensitive to environmental conditions than is the expression of morphological and physiological traitsoTraits that develop uniformly in a wide range of environments such as finger numbers are said to be canalizedoTraits that vary in response to environmental cues such as subsistence strategies are said to be plasticoEvery trait however results from the unfolding of a developmental program in a particular environmentNatural selection can shape developmental processes so that organisms develop different adaptive behaviours in different environmentsoThere is a misunderstanding that natural selection cannot create adaptations unless behavioural differences between individuals are caused by genetic differencesoIf this were true adaptive explanations of human behaviour must be invalid because there is no doubt that most of the variation in behavioural traits such as foraging strategies is not due to genetic differences but is instead the product of learning and culture2oBelief is false because natural selection shapes learning mechanism so that organisms adjust their behaviour to local conditions in an adaptive wayoEx Male soapberry bugs guard their mates when females are scarce but not when females are abundantIndividual males vary their behaviour adaptively in response to local sex ratioIn order for this flexibility in behaviour to evolve there had to be small genetic differences in male propensity to guard a mated female and small genetic differences in how mate guarding is influenced by local sex ratioIf such variation exists then natural selection can mold responses of males so that they are locally adaptiveIn any given population most of the observed behavioural variation is due to fact that individual males respond adaptively to environmental cuesoThe crucial point is that evolutionary approaches do not imply that differences in behaviours among humans are product of genetic differences between individualsUnderstanding How We ThinkEvolutionary analyses provide important insights about how our brains are designedoNatural selection hasnt just made our brains big it has shaped our cognitive abilities in very specific ways and molded the way we thinkEven the most flexible strategies are based on specialpurpose psychological mechanismsoA considerable body of empirical evidence indicates that animals are predisposed to learn some things and not othersoEx Rats quickly learn to avoid novel foods that make them sickBased solely on taste of a food that has made them sick not the foods size shape colour or other attributesMakes sense because rats live in a very wide range of environments where they frequently encounter new foods and usually forage at night when it is darkoThere are certain limits to the flexibility of this learning mechanism
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